1. Field of the Invention
The invention relates to still cameras and more specifically to such cameras with automatic ranging capabilities.
2. Description of the Prior Art
Various focus detectors or ranging systems have heretofore been proposed for use with cameras, to automatically determine a subject's distance from the camera and to enable automatic or manual distance adjustment of the camera's lens in accordance with the distance so determined. One of these known systems employs a flashlamp to produce a fixed quantity of light and suitable range detection circuitry to sense the quantity of flash light reflected by the subject to be photographed. The circuitry converts the sensed reflected light into an electrical signal and stores the signal in a storage capacitor; whereby the focus adjustment may be effected in accordance with the stored signal. However, use of a visible ranging flash may be undesirable because of the disturbing or disruptive effect it may have when photographing certain scenes which do not require flash illumination, e.g. religious ceremonies or theatre performances. For this reason, the use of infrared light has been suggested in the past in conjunction with automatic exposure control systems and automatic focus systems which rely on light emitted to the scene to be photographed.
In Simjian U.S. Pat. No. 1,866,581 a camera is focused automatically in response to the amount of light reflected by the subject from a fixed floodlight. Although the floodlight normally serves to provide the photographic illumination, Simjian suggests that it could be covered by an infrared filter. However, either the insertion or removal of this filter would necessitate recalibration of the electronic circuits.
Stimson U.S. Pat. No. 3,173,347, discloses a system that has two light sources; one for exposure and one for ranging. The camera has two photocells, one being sensitive to visible light or daylight and the other being sensitive only to infrared light. The photocells can be selectively interconnected to the measuring instrument so that the photocell sensitive to visible light is used for daylight operation and the photocell sensitive to infrared light is used for flash operation.
The present invention retains the advantages associated with using infrared or other radiation outside the normal sensitivity of the human vision for ranging, while using the same light source for both ranging and exposure illumination without the need to recalibrate the system when changing from one mode to the other.